1. Deserts

2. What causes a desert – Is there a global pattern?
The word “desert” – means deserted or literally uninhabited
Features of a typical desert
absence of soil and abundant plant life
barren rocky outcrops
steep angular slopes
common rock colors of tinted red and oranges
deserts definitely represent dry-dry-dry environments
What causes a desert – Is there a global pattern?

3. Two ways to produce deserts:
Global winds
high/low pressure systems
Blocking precipitation
Rain shadows

4. What global patterns show the distribution of deserts?
Air sinks (H)
Air
rises
(L)
Air sinks (H)
30O North Latitude
Equator
30O South Latitude

5. Desert created by a rain shadow
Dry Air
Precipitation
Rain
Shadow
Moving air
Dry Air
Sierra
Nevada
Mountains
Precipitation
Rain Shadow
Coast
Ranges
Evaporation
Delano
Santa
Barbara

6. High Pressure (air sinks) Equator
Rain Shadow deserts
30O N .
High Pressure (air sinks)
Equator
Low Pressure (air rises)
High Pressure (air sinks)
30O S

7. US RAIN SHADOWS
30O North

8. I Deserts Describe a least 3 common characteristics found in deserts
2. Describe the 2-ways deserts are formed
on the earth’s surface
3. Explain why Bakersfield is considered a
semi-desert region– what influences Bako’s
amount of precipitation?
Discuss with a friend
I will get an A on my exams and quizzes

9. Differences between topography and weathering
Coast Ranges
The Desert
Ppt > Evaporation
Ppt < Evaporation
Rounded hills with thick soil profiles supporting dominate chemical weathering
Angular cliffs, jagged mountains
unaltered rocks supporting
dominate mechanical weathering
Abundance of ephemeral streams carry water only when there is rain
Common year around
streams

10. Common Desert features produced by transportation of sediment by water
Alluvial fans
Bajada
Inselbergs
Playa Basins

11. Arial view of a “typical” desert
Water transported features
Alluvial fans:
a fan shaped deposit of
sediment protruding
from the mouth of a
canyon
Alluvial fans
Mountains
Bajada:
a collection of alluvial
fans that have coalesced
together
Inselberg
large bedrock “knobs”
that are raised above
sediment
Playa
Playa
Playa:
a flat basin area that
shows the remnant of
a “desert” lake – the
lake has evaporated

12. Continued erosion Cross sectional view of a desert landscape proximal
Alluvial fans
Playa basin
proximal
distal
Continued erosion
Inselberg
Bedrock
Alluvial fans – coarse thin deposits proximal part of fan
finer deposits at distal part of fan
Playa basin – fine lake bed deposits (water drains the alluvial fan)

13. I Deserts Describe the following common desert features:
alluvial fan playa basin
inselberg bajada
Discuss with a friend
I will get an A on my exams and quizzes

14. Transportation of sediment by Wind
Bed load – saltation processes
Suspended loads
Types of desert features from wind erosion
Deflation, blowouts, desert pavement
Wind abrasion
Various types of wind deposits
vantifacts
sand dunes

15. Moving sand grains by wind – the bed load
Saltation – wind blown sand “jumps” in the wind
Wind must be strong enough to overcome
inertia
Saltation ends when wind is weak
Grains are not moved very far
“sandblasting”

16. The suspended wind blown sediment
Finer sediments (silt-size and smaller) is lifted and
suspended within the atmosphere
Wind storms – sand blast the windshield
Dust storm- suspended load
Saltation

17. Wind Erosion – results of the power of wind
Deflation – the lifting or removal of material by winds
Dependent on wind velocity
Dependent on grain-size to be picked up
Deflation begins
Deflation continues
to remove finer particles
Heavier particles left on
desert floor – deflation
Ends – Desert Pavement

18. Examples of desert pavement produced by
deflation processes

19. Wind abrasion – the act of sand-blasting
Ventifacts- rocks that have been shaped by sandblasting
The rock sits there for many years
Abrasion of wind-blown sand constantly shapes
the rock

20. Ventifacts

21. I Deserts What is the primary way sediment is
transported in desert areas?
Describe the following processes
saltation deflation
3. How is desert pavement created
4. What is a ventifact? – how are these
created?
Discuss with a friend
I will get an A on my exams and quizzes

22. Wind Deposits – Sand Dunes
Sand dunes – an accumulation of sand grains that reflect the consistent
wind velocity and wind directions
Typical formation of a sand dune
dependant on wind direction and wind velocity
quantity of sand
About 28 degrees

23. Types of Sand dunes Barchan dune – crescent like shapes with horns
pointed towards the wind
Longitudinal Dunes – sand grains are
blown parallel to wind direction- supplies
are moderate
Transverse dunes – sand ridges are
oriented at right angles to wind – sand is
plentiful and winds are consistent

24. Longitudinal Dunes Barchan Dunes Transverse Dunes Wind direction